diff --git a/default.nix b/default.nix
index f26de54eab39ba3adff824db3daff7b3eedf52ed..bc6a0884559432f6b8c0c65473530de99154bbd5 100644
--- a/default.nix
+++ b/default.nix
@@ -72,7 +72,8 @@ in
           pyrsistent
           configparser
           eliot
-          foolscap >= 21.7.0
+          foolscap
+          collections-extended >= 2.0.2
 
           # undetected cryptography build dependency
           # https://github.com/DavHau/mach-nix/issues/305